Genetic disorders of the mitochondrion represent the most common collection of inborn errors of metabolism, impacting over 1:4000 live births. They are characterized by an inherited defect in the respiratory chain, whose blockade leads to multisystem organ failure and inevitable death. Although there has been tremendous progress in elucidating the molecular bases of these disorders, with over 100 disease genes identified to date, not a single therapy has been proven to be useful. Because so many different genes can be mutated in these disorders, traditional enzyme replacement therapy is unlikely to be a useful approach. We propose a potentially generic therapeutic strategy that that aims to target the common biochemical pathway that is altered in mitochondrial disorders. Our approach is inspired by nature: a number of microbes, protozoa, and fungi have evolved relatively simple biochemical innovations that allow them to survive without respiratory chains. We propose to use computational genomics to systematically scan the thousands of sequenced bacterial genomes to identify those lacking complete respiratory chains, and then to use a mix of bioinformatics, bacterial genetics, and chemical biology to systematically identify the proteins and small molecules that endow them an ability to survive without a complete respiratory chain. We will create a library of such polypeptides and natural products and evaluate their ability to alleviate pathology in human cellular models of mitochondrial disease. If successful, this project will yield an entire pipeline of small molecules and proteins that may represent the starting point for a new class of therapeutics for these disorders. PUBLIC HEALTH RELEVANCE: The mitochondrial respiratory chain disorders collectively represent the most common inborn error of metabolism. The prevalence is estimated to be 1:4000 live births. These disorders can present in childhood or in young adulthood and are difficult to diagnose and manage. At present there is not a single proven therapy. The proposed project aims to develop a new therapeutic approach to these disorders.